Ethanol has widespread application as an industrial chemical, gasoline additive or straight liquid fuel. As a fuel or fuel additive, ethanol dramatically reduces air emissions while improving engine performance. As a renewable fuel, ethanol reduces national dependance on finite and largely foreign fossil fuel sources while decreasing the net accumulation of carbon dioxide in the atmosphere.
Citric acid has widespread application as a food additive to adjust the pH of foods, as a synergistic antioxidant, and as an industrial chemical in the manufacture of alkyd resins, as a plasticizer and as a sequestering agent to remove trace metals. Isopropanol is also used as an industrial chemical as a solvent, in the composition of antifreeze, as well as in the manufacture of quick-drying inks and oils. Butanol is also used as an industrial chemical as a solvent, including use in industrial cleaning compounds and the like.
Biomass includes materials containing cellulose, hemicellulose, lignin, protein and carbohydrates such as starch and sugar. Common forms of biomass include trees, shrubs and grasses, corn and corn husks as well as municipal solid waste, waste paper and yard waste. Biomass high in starch, sugar or protein such as corn, grains, fruits and vegetables are usually consumed as food. Conversely, biomass high in cellulose, hemicellulose and lignin are not readily digestible and are primarily utilized for wood and paper products, fuel, or are disposed of.
Ethanol and other chemical fermentation products typically have been produced from sugars derived from feedstocks high in starches and sugars, such as corn. While the discussion of fermentation products described herein describes the method and apparatus of the current invention using the example of how the current invention is used to produce ethanol, it will be appreciated by those skilled in the art that the current invention also has application to other fermentation products, including citric acid, butanol and isopropanol and that references to ethanol encompass these other fermentation products.
Recently, the conversion to ethanol of polymeric hexose and pentose sugars in cellulose and hemicellulose has been achieved. See U.S. Pat. No. 4,349,628 to English et al; see also U.S. Pat. No. 4,400,470 to Zeikus et at; U.S. Pat. No. 5,000,000 to Ingram et al; U.S. Pat. No. 5,028,539 to Ingram et al; and U.S. Pat. No. 5,162,516 to Ingram et al, all of which are incorporated herein by reference.
Despite these advancements, certain "non-virgin" forms of biomass have not been successfully utilized in the production of ethanol. For example, municipal solid waste (MSW) as a complex mixture of organic and inorganic materials (approximately 45% paper, 15-20% food and yard waste, 3-5% wood, 12-18% metal and glass, 5-7% plastics and textiles and 5-20% other materials) has certain constituents such as ferrous, non-ferrous and heavy metals, inks, dyes, plastics and clays as well as solvent, pesticide and herbicide residues which can have a deleterious effect on its conversion to ethanol. Similarly, other sources of non-virgin biomass also typically contain deleterious materials which inhibit or prevent their conversion to ethanol.
Disposing of MSW and other non-virgin biomass in an economic and environmentally sound manner is a matter of public concern. Various waste disposal, sorting and recovery systems are known in the art. See e.g., U.S. Pat. No. 2,257,567 to Matanovich-Manov et al; U.S. Pat. No. 3,557,685 to Schroering; U.S. Pat. No. 3,804,248 to Talamantz; U.S. Pat. No. 3,878,995 to Nash; U.S. Pat. No. 3,888,351 to Wilson; U.S. Pat. No. 4,187,775 to Flender; U.S. Pat. No. 4,553,977 to Fry; U.S. Pat. No. 4,561,860 to Gulley et al; U.S. Pat. No. 4,662,569 to Acker; U.S. Pat. No. 4,667,291 to Weitzman et al; U.S. Pat. No. 4,894,066 to Castelli; U.S. Pat. No. 5,134,944 to Keller et al and U.S. Pat. No. 5,250,100 to Armbristor, all of which are incorporated herein by reference. The most common disposal techniques currently utilized by industrial societies are recycling, waste-to-energy conversion and landfilling. Each of these methods has certain disadvantages associated therewith. These disadvantages, including economic and environmental shortcomings, make these techniques less than wholly desirable as a means of disposal.
Recycling can be accomplished through "source separation" wherein wastes are segregated into bins, containers, or "blue bags" by the generator. Alternatively, mixed wastes may be manually and mechanically separated into its constituents without pre-sorting. Recycling programs, although popular, are expensive and inefficient; managing only about 15-25% of municipal solid waste streams. The significant portion of waste materials which cannot be recycled continue to require alternative disposal with attendant infrastructure and cost.
Waste-to-energy conversion is typically accomplished by either preparing from wastes a fuel product for incineration or by "mass-burning" it. These technologies have largely fallen out of favor due to their high cost and negative environmental impact. Moreover, serious air emission and residue toxicity issues remain unresolved giving rise to health and safety concerns.
Landfilling as well, has serious environmental issues associated therewith. For example, landfill gas emissions can be dangerous and toxic leachate can pollute groundwater. Further, landfills often create noxious odors. This technology, although low in cost, results in wasting valuable land, energy and material resources. In many areas where land, energy and material resources are highly valued, there is a trend toward banning the landfilling of wastes.
Various forms of biomass have potential as renewable feedstocks for ethanol production due to their enormous availability and low cost. However, prior attempts to dispose of non-virgin biomass through fermentation to ethanol have been largely unsuccessful. It would therefore be desirable to provide a method and apparatus for the production of ethanol from biomass containing deleterious materials therein, thereby providing an alternative waste disposal technique and overcoming the shortcomings associated with the prior art.